System for providing for the generation and visual indication of characters



Oct. 11, 1966 A. F. BosclA ETAL 3,278,794

SYSTEM FOR PROVIDING FOR THE GENERATION AND VISUAL INDICATION OF CHARACTERS Filed March 22, 1962 United States Patent O SYSTEM FOR PROVIDING FOR THE GENERATION AND VISUAL INDICATIQN F CHARACTERS Archie F. Boscia, Gardena, and Franz Worth, Van Nuys,

Calif., assignors to The Electrada Corporation, Culver Clty, Calif., a corporation of Delaware Filed Mar. 22, 1962, Ser. No. 181,721 8 Claims. (Cl. 315-21) The present invention relates to character generators, and more particularly to a monoscope vacuum tube suitable for producing video signals of preselected characters to be displayed by a cathode ray type display tube.

At the present time, it is very frequently desirable to be able to rapidly pr-oduce video signals for controlling a cathode ray tube whereby preselected characters such as letters, numbers, and various symbols may be displayed upon the face of a cathode ray vacuum tube. One means of accomplishing this is to employ a monoscope vacuum tube lhaving a target which is positioned so that an electron Ibea-m may be directed against the target to produce secondary emission of electrons. A collector ring is disposed adjacent to the target and is maintained sufficiently positive with respect thereto to collect the secondarily emitted electrons `and produce a current flow from the target to the collector ring. The target may be divided into a plurality of sections with each section having one of the characters to be displayed. Thus, if the electron beam is scanned across a particular section, the current flow from the target to the collector ring will be a video signal corresponding to the character.

Heretofore, monoscope vacuum tubes of the foregoing variety have employed targets consisting of a highly secondary emissive material such as aluminum. The characters have been printed on the target by employing a material such as printers ink that is a poor secondary emitter of electrons. Thus, when the electron beam is directed against the ink, there will be a minimum amount of secondary emission, whereas when the beam is incident on the aluminum, there will be a maximum amount of secondary emission.

Tubes of this type have been very effective to produce useful signals. However, since there is some secondary emission from the coating material or ink, there is an appreciable amount of current flow when the electron beam is directed onto the character. This decreases the maximum signal strength and `decreases the signal-tonoise ratio. In addition, it has been found very difficult if not impossible to precisely confine the application of the ink to the characters. As a result, objectionable amounts of the coating material or ink are dispersed onto the uncoated portions of the tar-get to thereby contaminate the surface of the target. This results in a further reduction in the signal strength and an objectionable decrease in the signal-to-noise ratio. Moreover, since it is extremely difficult if not impossible to print the characters with a high degree of precision, there are some errors in the positioning of the characters and major errors in the shape and definition of the characters.

It is now proposed to provide a monoscope vacuum tube for generating video signals of preselected characters which will overcome the foregoing difficulties. More particularly, it is proposed to provide a monoscope tube which will provide signals having greater amplitude and contrast, higher signal-to-noise ratio, and a more precise definition of the character. This is to be accomplished b-y providing a monoscope vacuum tube having a target member disposed immediately adjacent a collector ring whereby a current may iiow from the target to the collector, as a result of secondary emission from the target to the collector ring. The target member preferably consists of a material such as aluminum which Patented ct. l1, 1966 ICC produces a large amount of secondary emission when bombarded by a beam of electrons. The desired preselected characters are formed on the target so that no secondary emission can occur when bombarded by the beam of electrons. Although these characters may be of various types, in the present instance they consist of apertures that extend completely through the target member and have shapes corresponding to the characters. These apertures are preferably formed by a very precise means such as a high precision etching process. It has been found that such an etching process can not only position Vanddeiine the characters with far greater accuracyrtharn has heretofore been possible, but can also be performed without contaminating the target member or in any way affecting the amount of secondary emission from the portions immediately adjacent the characters. Since there can be no secondary emission when the electron beam is passing entirely through one of the apertures, the resultant signal will be of greater amplitude, more precise, and freer from any undesired noise These and other features and advantages of the present invention will become apparent from reading the following detailed description of one embodiment thereof, particularly when taken in connection with the drawings, wherein like reference numerals refer to like parts and wherein FIGURE 1 is a transverse cross sectional view of a monoscope tube embodying the present invention, together with a block diagram showing means for controlling and utilizing the tube.

FIGURE 2 is a perspective view of a fragment of a target member in the tube of FIGURE 1.

FIGURE 3 is a graph of several wave forms suitable for use in controlling and utilizing the tube of FIGURE 1.

Referring to the drawings in more detail, the present invention is embodied in a monoscope vacuum tube 10 for generating video signals corresponding to various preselected characters such as letters, numbers, punctuation marks, symbols, etc. The resultant video signals are suitable for use in the control of the electron beam in a conventional cathode ray vacuum tube 12 having a phosphorescent screen thereon that may be scanned or bombarded by a stream of electrons so as to luminesce with visible light proportional to the intensity of the electron beam, The video signals may be effective to cause the electron beam to scan across the screen so as to cause the preselected characters to appear as a visible display on the screen. By Way of example, reference may be had to copending application, Serial Number 79,884, now U.S. Patent No. 3,166,636 entitled Data Composer and led in the names of Rutland et al. and assigned to Electrada Corporation, for a disclosure of a system employing a monoscope for generating video signals that are utilized for controlling a cathode ray vacuum tube.

The present monoscope tube 10 includes an outer envelope 16 which is hermetically sealed to form an air tight enclosure particularly adapted for containing a high vacuum therein. Although this envelope 16 may be of any suitable material, it has been found desirable to employ a dielectric material such as glass. In the present instance, this envelope 16 includes a barrel or central portion 18, a reduced end or neck 20, and a target end 22. The barrel, or central portion 18 is preferably substantially cylindrical so as to be of uniform diameter. The reduced end or neck 20 preferably blends from the barrel or central portion 18 into a diameter that is slightly smaller than the inside diameter of a base 24. The end of the neck 20 may thus be hermetically sealed inside of the base 24 so that electrical connector pins 26 on the base 24 may t into a suitable socket and thereby form electrical paths from the socket into the electrode elements disposed inside of the envelope 16. The target end 22 preferably includes a substantially plane end wall 28 that has a layer 25 of phosphorescent material to thereby form a screen. These phosphors are particularly adapted to luminesce with visble light when bombarded by an electron stream to thereby form a luminescent pattern or display that may be observed through the end wall 28.

A conventional electron gun 30 may be mounted on the base 24 so as to be disposed in the neck 20 and aimed yaxially of the tube toward the end wall 28. The electron gun 30 includes means which are connected with one or more of the electrical pins 26 for generating and accelerating a -large number of electrons axially of the gun 30 and focusing the electrons into a small well defined beam 32 that will be traveling at an adequate velocity to traverse the entire length of the tube 10 and collide with the phosphors and cause them to lumlnesce. In order to control the electron beam 32 and the direction it is traveling, suitable deflection means 34 may be provided adjacent the end of the electron gun 38. Although the deflection means 34 may be of any suitable variety, in the present instance they are of the so-called electro-static variety and include a pair of horizontal deflection plates 36 and a pair of vertical deflection plates 38. The plates in each pair are separated from each other by a small space disposed in substantial -alignment with the axis of the electron gun 30 and will cause deflection of the beam 32 in proportion to the potential difference across the space. In order to energize the plates in each pair, the plates are all connected to a deflection amplifier 48. This amplifier 40 may be of a well known variety suitable for applying control potentials to the deflection plates 36 and 38.

In order to facilitate the preparation of video signals of preselected characters, a signal generating structure 42 may be disposed in the barrel portion 18 adjacent the end wall 28. The present structure 42 includes a target member 44 and a collector 46. Although the target member 44 may be of any desired configuration, in the present instance it is a plane member consisting of a conductive material which will be effective to radiate a large number of secondary electrons when bombarded by the beam 32 of primary electrons. By way of example, it has been found that aluminum is well suited for this purpose. The target member 44 is preferably rigidly supported substantially parallel to the screen 22 and reasonably close thereto. It will thus be seen that the electron beam 32 from t-he gun 30 will travel through the barrel portion 18 so as to arrive at the target member 44 substantially normal to the plane thereof. Any of these electrons that strike the plate 44 will produce a secondary emission of large quantities of electrons. These secondary electrons will initially tend to travel from the target member 44 back toward the gun 30. Any electrons that are not incident on the target member 44 will pass onto the end wall 28 and cause the phosphors thereon to luminesce.

Although the collector ring 46 may be of any desired variety, in the present instance it comprises a ring that is disposed 'inside of the barrel portion 18 close to but spaced from the target member 44 and substantially concentric with the axis of the electron gun 30. More particularly, the present collector ring 46 is a cylindrical member formed by depositing a conductive coating on the interior of the barrel 18. The coating may consist of any suitable material such as conductive carbon. It may thus be seen that the secondarily emitted electrons may be attracted to the collector 46 whereby a current may flow backwardly from the target member 44 to the collector ring 46. Electrical contacts 47 and 48 may be connected with the target 44 and collector ring 46 to permit this current to llow outside of the tube.

In order to facilitate the generation of the video signals of preselected characters such as letters, numbers, punctuation marks, symbols, etc., the characters may be formed on the target 44. Each of the characters are disposed in areas or sections that are arranged in a suitable A configuration such as a square matrix having eight horizontal rows and eight vertical columns. This will provide a total of 64 areas or sections in which the characters may be disposed. Since 8 is the third power of 2, any given row may be precisely identified by three binary bits any given column may also be precisely identified by three binary bits. Thus the position of any character in the matrix may be precisely defined by employing two groups of 3 binary bits each.

As may be seen in FIGURE 3, which is a perspective View of a small portion of the target member 44, the cha-racters are preferably defined by apertures or openings that extend completely through the target member 44. Although these openings may be formed by any suitable means such as a machining or punching operation, it has been found that a precision etching process is well suited for this purpose. In such .a process, the surface of a blank target member is covered with a protective coating that will not be attacked by the etchant. Portions of the coating are then removed to correspond t-o the characters to be formed and the assembly is immersed in an etchant bath until the etchant has eaten -completely through the target member 44. Following this the protective coating is removed. It has been found that processes of this nature can form the characters to tolerances of less than one thousandth (0.001) of an inch. In addition, after removal of the protective coating, the surface of the target member 44 will be uniformly free of any form of contamination.

It may thus be seen that when the target member 46 is disposed in the barrel portion 18 in alignment with the electron gun 30, the deflection plates 36 and 38 can cause the electrons in the electr-on beam 32 to travel completely through one of the characters or against the surface of the target member 44. When the electron beam is aimed at an opening formed by a character, none of the electrons in the beam 32 will be incident on the surface of the target member 44. Consequently there will be no secondary emission from the target member 44 and there will be no current flowing from the target member 44 to the collector ring 46. However, when the beam 32 is aimed at a portion of the target member 44 surrounding a character, the electrons will produce large quantities of secondarily emitted electrons that will result in a current flow from the target member 44 to the collector ring 46.

In order to employ the present monoscope tube 10 for t generating video `signals suitable for controlling the cathode ray tube 12, the electron gun 30 may be interconnected with suitable energizing means including for example, a 2 kilovolt power source 50. In addition, the horizontal and vertical deflection plates 36 and 38 may be interconnected with the deflection amplifier 40. The present deflection amplifier 40 has a first input 52 that receives position signals and a second input 54 that receives sweep signals. The position signals Will be a first pulse having an amplitude corresponding to the vertical position of the character in the matrix and a second pulse having an amplitude corresponding to the horizontal position of the character in the matrix. As previously stated, each of these pulses may be derived from groups of three binary bits. The sweep signals will include a signal such as a saw tooth wave and a sine or periodic wave having a frequency that is substantially higher than the rst wave.

The deflecti-on amplifier 48 will be effective to combine the signals from the two inputs 52 and 54 and to form a vertical deflection signal and a horizontal deflection signal. The horizontal deflection signal as shown in FIG- URE 3 includes a D.C. level that corresponds to the vertical column that the character is in and will position the electron beam 32 on one side, for example the left side, of the `area or section containing the character. This signal also includes a saw tooth component that will cause the electron beam 32 to scan horizontally across the area or section containing the character, for example from left to right.

The vertical deflection signal as shown in the lower half of FIGURE 3 includes a D.C. level that corresponds to the horizontal row containing the area or section in which the character is disposed. This signal will cause the beam to be centered in the middle of the row but it has a periodic component such as a sine wave that will cause the beam 32 to be deflected vertically through the area or section containing the character.

It may thus be seen that the position signals at the input 52 will cause the electron beam 32 to be directed to the area or section at the intersection of a column and a row containing the character to be reproduced. At the same time, the sweep signals at the input 54 will cause the beam 32 to scan slowly across the area in Va horizontal direction. Thus, the beam 32 will progressively scan the entire area containing the preselected character. As the beam 32 scans across an area containing a character, the electrons will alternately pass through the opening forming the character or be incident upon the surface of the target 44. The electrons that pass through the opening will strike phosphorescent layer 25 on the end wall 28 and cause the phosphors to generate visible light. As a result of the scanning of the beam 32 across the area containing the character, the electrons passing through the opening form an electron silhouette whereby the light pattern will be an image of the character. Thus, a person looking at the end wall 28 may see the character. Since the characters will be visible it will be a simple and rapid process to adjust the deflection means so that the beam 32 is accurately positioned to scan an area with the character to be reproduced.

When the electrons are passing through the opening, Ithere will be no reverse current owing from the target 44 to the collector ring 46. However, when the electron beam 32 is incident upon a portion of the target 44 immediately surrounding the characters, there will be a large amount of secondary emission. The collector ring 46 is connected to a positive source 50 on the order of 30 to 100 volts so that the secondary electrons will flow from the target 44 to the collector 46. It will thus be seen that the current flow from the target 44 to the collector 46 will be a video signal that is a function of the character being generated.

To utilize this signal for controlling the cathode ray tube 12, the target 44 and/or collector 46 may be connected to an .input impedance in a conventional video amplifier 60 where the signal will be converted to a voltage signal and will be amplied, This amplified signal may then be fed into the control means for the cathode ray tube 12.

The electron beam 32 in the tube 10 is scanned horizontally across the area of the target member 44 containing the characters at a uniform velocity while being scanned vertically in a sinusoidal or periodic manner.

The beam in the cathode ray tube 12 will also scan horizontally across the area of the face thereof where the character is to be produced. The beam in the tube 12 will scan across the area in synchronism with the beam 32 in the tube 10. In addition, the beam in the cathode ray tube 12 will scan vertically in a periodic manner identical to the scanning in the tube 10. It will be seen the current from the target 44 to the collector ring 46 will be effective to modulate the electron beam in the cathode ray tube 12 whereby the character will be reproduced on the face of the tube 12.

Although only a single embodiment of the present invention is disclosed and described, it will be readily apparent to persons skilled in the art that numerous changes and modifications may be made thereto without departing from the spirit of the invention. Accordingly, the foregoing disclosure and description thereof are for illustrative purposes only and are not to limit the invention, which is defined only by the claims which follow.

6 We claim: 1. In a device of the class described for generating video signals of preselected characters, the combination of an electron gun for projecting a beam of electrons,

a target member disposed in alignment With said gun for having the electrons in said beam directed thereagainst, said target member including a plurality of individual areas, each of said area including an aperture corresponding to one of said characters,

means for individually scanning said electron beam across pre-selected areas of the surface of said target member and the aperture therein, and

means for utilizing the current flowing in said target member to provide said video signal.

2. A vacuum -tube for generating video signals of preselected characters, the combination'of an electron gun disposed adjacent one end of said vacuum tube for projecting a beam of electrons substantially axially of said tube toward the opposite end thereof,

a target member disposed in substantial alignment with said gun for having the electrons in said beam directed thereagainst, said target member including a plurality of apertures extending through said target member to permit said electrons to pass through said target member without impinging thereon, said apertures having shapes corresponding to the shapes of said characters and being arranged in a matrix so that each of said characters will be disposed in a separate section of said target member, and

means for sensing the current ow through said target member to provide said video signal.

3. A vacuum tube for generating video signals of preselected characters, the combination of an electron gun disposed adjacent one end of said vacuum tube for projecting a beam of electrons substantially axially of said tube toward the opposite end thereof,

a target member disposed in substantial alignment with said gun for having the electrons in said beam directed thereagainst, said target member including a plurality of apertures therethrough having shapes corresponding to said characters, said apertures being arranged in a matrix so that each of said characters will be disposed in a separate section of said target member,

means for obtaining a scanning by said beam of electrons of individual ones of the sections in said target member,

and means for sensing the current flow through said target member while said beam is scanning the individual ones of said sections to thereby provide said video signal of the character in said section.

4. A vacuum tube for generating video signals of preselected characters, the combination of an electron gun for projecting a beam of electrons substantially axially of said tube,

a target member disposed in substantial alignment with said gun for having the electrons in said beam directed thereagainst with suicient velocity to produce secondary emission of electrons from said target member, said target member containing a plurality of apertures having shapes corresponding to the shapes of said characters to permit the electrons to pass through said target member Without impinging thereon, and

a collector electrode disposed adjacent said target member for collecting said secondarily emitted electrons.

5. A vacuum tube for generating video signals of preselected characters, the combination of an electron gun for projecting a beam of electrons substantially axially of said tube,

a target member disposed in substantial alignment with said gun for having the electrons in said beam directed thereagainst With sucient velocity to produce secondary emission of electrons from said target member, said target member containing aplurality of apertures in a matrix such that each of said apertures is in a separate section, each of said apertures extending completely through the target member so that electrons directed toward an aperture will pass through the aperture and will not produce secondary emission from the target,

means for scanning said electron beam across the sections containing the characters to be reproduced, and collector electrode disposed adjacent said target member for collecting said secondarily emitted electrons.

A vacuum tube for generating video signals of preselected characters, the combination of an electron gun for projecting a beam of electrons substantially axially of said tube,

a target member disposed in substantial alignment with a collector electrode disposed adjacent said target member for collecting said secondarily emitted electrons, and

means for scanning said electron beam across said sections containing the characters to be reproduced. A vacuum tube for generating video signals of preselected characters, the combination of an electron gun for projecting a beam of electrons substantially axially of said tube,

target member disposed in substantial alignment with said gun for having the electrons in said beam directed thereagainst with suicient velocity -to produce secondary emission of electrons from said target member, said target member containing a plurality of apertures having shapes that are the same as the shapes of said characters, said apertures being arranged in a matrix with each of said characters being disposed in a Vseparate section of the matrix,

a collector electrode disposed adjacent said target member for collecting said secondarily emitted electrons,

means for scanning said electron beam across the sections containing the characters to be reproduced,

and

means interconnected with said collector and said target member for sensing the current ow between said collector and target member.

8. A vacuum tube for generating video signals of preselected characters, said tube comprising the combination of an airtight envelope enclosing a vacuum space,

an electron gun disposed at one end of said envelope for directing a beam of electrons across said space,

a phosphorescent screen disposed on the opposite end of said envelope in substantial alignment with said electron gun for luminescing with visible light when said electrons are incident thereon,

a target member in said envelope, positioned between said electron gun and said screen and consisting of a material that produces secondary emission of electrons when bombarded with said beam, said target member including a plurality of apertures arranged in a matrix with each of said apertures being disposed in a separate section, each of said apertures having a cross-sectional shape that is the same Vas the shape of a character and that extends completely through said target member to allow electrons directed at said apertures to pass through said apertures without producing secondary emission from the target and to impinge on said screen to produce a luminescent pattern having the same shape as said aperture,

means for scanning said electron beam across the seca collector disposed adjacent said target member for collecting said secondarily emitted electrons.

References Cited by the Examiner UNITED STATES PATENTS 2,496,633 2/ 1950 Llewellyn S15-8.5 2,689,314 9/1954 Gunderson 313--86 X 2,781,171 2/1957 Hagen S15-8.6 X 2,784,251 3/1957 Young et al. 315-1 3,047,858 7/ 1962 McNaney.

FOREIGN PATENTS 904,115 2/ 1954 Germany.

DAVID G. REDINBAUGH, Primary Examiner.

ARTHUR GAUSS, Examnier. S. GARDNER, J. E. BECK, I. A. GALLAGHER,

Assistant Examiners. 

4. A VACUUM TUBE FOR GENERATING VIDEO SIGNALS OF PRESLECTED CHARACTERS, THE COMBINATION OF AN ELECTRON GUN FOR PROJECTING A BEAM OF ELECTRONS SUBSTANTIALLY AXIALLY OF SAID TUBE, A TARGET MEMBER DISPOSED IN SUBSTANTIAL ALIGNMENT WITH SAID GUN FOR HAVING THE ELECTRONS IN SAID BEAM DIRECTED THEREAGAINST WITH SUFFICIENT VELOCITY TO PRODUCE SECONDARY EMISSION OF ELECTRONS FROM SAID TARGET MEMBER, SAID TARGET MEMBER CONTAINING A PLURALITY 